How To Check the Distributor Cap

The distributor cap is an important component of your vehicle.  Its primary role is to distribute high-voltage electricity from the ignition coil to all the spark plugs.  The sparks cause the engine’s cylinders to fire in the correct order, thus starting the engine.  The cap is usually made of hard and durable plastic and can withstand high-voltage electric charges, vibration, and heat.  Yet, it needs to be regularly checked because a fault or problem in the distributor cap can actually prevent your car from starting at all.  This article describes the some of the common problems to look for when checking your distributor cap.

The first thing you need to do is to locate the distributor cap.  It is fairly easy to find because it looks like an octopus with wires as its tentacles.  Those wires are from your engine’s cylinders.  If you have trouble finding your distributor cap, look for a spark plug wire.  Needless to say, spark plug wires connect to the spark plugs, which are all over your engine.  If you follow the wire from one spark plug, it will lead you directly to the distributor cap.

Once you’ve found the distributor cap, try to move it back and forth.  If it does move, either the screws are loose or the gasket is worn and needs to be replaced.  Check the screws and tighten them if needed.  If the gasket is worn, replace it.

Next, remove the distributor cap.  Check the cap for the following:

  • Cracks – The cap is made of durable plastic, but can eventually give in to too much heat or vibration.  Check the cap for signs of wearing, aging, or cracking.
  • Carbon tracking – The accumulation of carbon deposits in the distributor cap indicates a malfunction in the plug wires or in the spark plugs, resulting in increased resistance. Carbon deposits are hard to remove and, worse, can conduct electricity.  So, if there are carbon deposits in your distributor cap, replace the cap.
  • Moisture, debris, oil, dirt, and other contaminants – Water is a conductor and can reroute the electricity directly to the vehicle’s body instead of through the spark plug.  Without the spark, the fuel in the cylinders will not ignite.  All other contaminants can cause the same problems, so make sure that the distributor cap is clean.
  • Wearing in the rotor – If the rotor is worn, charred, or pitted, it needs to be replaced with a new one immediately.
  • Pitting, wearing, or charring in the terminals – Pitted, worn, or charred terminals are inefficient in conducting electricity.  If the terminals are in such a condition, you may need to replace the distributor cap.

Also, check the rotor and make sure that it is screwed securely in place.  Too much vibration from the engine can cause the screws to fall out and misalign the rotor.  No ignition can happen if the rotor is misaligned.  A dust cover protects the rotor from debris coming from the housing belt area.  If dust or other debris enters the distributor cap, it can cause poor or no sparks.  So, also make sure that the dust cover is firmly fastened in place.

Next time you perform a scheduled check-up of your car, always include checking the distributor cap.  Knowing what to check for will always be a big help to you in preventing unnecessary and costly repairs.


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